Much of refinery processing involves reaction of refinery streams in a hydrogen atmosphere. In order to maximize conversion efficiencies and to maintain catalyst life, excess hydrogen is generally used in the catalytic conversion processes, with the unreacted hydrogen being recovered, purified and repressurized for use as a recycle stream. Such recycle processes are costly, both in energy and in equipment. Some progress has been made in developing methods for using a single hydrogen loop in a reaction process having at least two stages.
In conventional hydroprocessing, it is necessary to transfer hydrogen from a vapor phase into the liquid phase where it will be available to react with a petroleum molecule at the surface of the catalyst. This is accomplished by circulating very large volumes of hydrogen gas and the oil through a catalyst bed. The oil and the hydrogen flow through the bed and the hydrogen is absorbed into a thin film of oil that is distributed over the catalyst. Because the amount of hydrogen required can be large, 1000 to 5000 SCF/bbl of liquid, and the amount of catalyst required can also be large, the reactors are very large and can operate at severe conditions, from a few hundred psi to as much as 5000 psi and temperatures from around 400xc2x0 F. to 900xc2x0 F.
U.S. Pat. No. 6,224,747 teaches hydrocracking a VGO stream in a hydrocracking reaction zone within an integrated hydroconversion process. Effluent from the hydrocracking reaction zone is combined with a light aromatic-containing feed stream, and the blended stream hydrotreated in a hydrotreating reaction zone. The hydrocracked effluent serves as a heat sink for the hydrotreating reaction zone. The integrated reaction system provides a single hydrogen supply and recirculation system for use in two reaction systems. There is no temperature control between the hydrocracking reaction zone and the hydrotreating reaction zone, however.
U.S. Pat. No. 3,592,757 (Baral) illustrates temperature control between zones by means of heat exchangers, as in the instant invention. Baral does not employ a single hydrogen loop, as does the instant invention. Baral discloses a hydrofiner (similar to a hydrotreater) operating in series with a hydrocracker, with a fraction of the product fed to a hydrogenator. A gas oil feed is fed with both make-up and recycle hydrogen to a hydrofiner. A recycle stream and additional recycle hydrogen are added to the hydrofiner product stream, and the mixture is fed to a hydrocracker. The hydrocracker product stream is cooled and separated into a vapor and a liquid stream. The vapor stream is passed to a recycle hydrogen compressor recycle to the hydrofiner. The liquid stream is fractionated into a top, middle, and bottom stream. The bottom stream is recycled to the hydrocracker. The middle stream is mixed with hydrogen from a make-up hydrogen compressor and directed to a hydrogenator. Hydrogen recovered from the hydrogenator is compressed in a stage of the make-up hydrogen compressor and directed to the hydrofiner.
U.S. Pat. No. 5,114,562 (Haun et al.) teaches a two-stage hydrodesulfurization (similar to hydrotreating) and hydrogenation process for distillate hydrocarbons. There is heat exchange between the two stages, but a single hydrogen loop is not employed. Two separate reaction zones are employed in series, the first zone for hydrodesulfurization and a second zone for hydrogenation. A feed is mixed with recycled hydrogen and fed to a desulfurization reactor. Hydrogen sulfide is stripped from the desulfurization reactor product by a countercurrent flow of hydrogen. The liquid product stream from this stripping operation is mixed with relatively clean recycled hydrogen and the mixture is fed to a hydrogenation reaction zone. Hydrogen is recovered from the hydrogenation reactor and recycled as a split stream to both the desulfurization reactor and the hydrogenation reactor. The hydrogen from the stripping operation is passed through a separator, mixed with the portion of the recycled hydrogen directed to the hydrogenation reactor, compressed, passed through a treating step and recycled to the hydrogenation reactor. Thus, the hydrocarbon feed stream passes in series through the desulfurization and hydrogenation reactors, while relatively low pressure hydrogen is provided for the desulfurization step and relatively high pressure hydrogen is provided for the hydrogenation step.
The instant invention is directed to temperature control between hydrocracking and hydrotreating zones, employing a single hydrogen loop.
A VGO stream is initially hydrocracked in a first-stage hydrocracking reaction zone within an integrated hydroconversion process. The integrated hydroconversion process possesses at least one hydrocracking stage and at least one hydrotreating stage. Effluent from the first-stage hydrocracking reaction zone is combined with a light aromatic-containing feed stream, and the blended stream is hydrotreated in a second stage, which comprises a hydrotreating reaction zone. Heat exchange occurs between the first-stage hydrocracking reaction zone and the second-stage hydrotreating reaction zone, permitting the temperature control of the first-stage hydrotreating zone. The temperature of the first-stage hydrotreater is lower than that of the first-stage hydrocracker. This improves the aromatic saturation of the converted hydrocarbons and also allows the catalyst of the first-stage hydrotreating zone to be different from the catalyst in subsequent hydrocracking zones that may be present. In one embodiment, the effluent from the first-stage hydrotreater is heated in an exchanger, then passed to a hot high pressure separator, where overhead light ends are removed and passed to a cold high pressure separator. In the cold high pressure separator, hydrogen and hydrogen sulfide gas is removed overhead and materials boiling in the gasoline and diesel range are passed to a fractionator. Hydrogen sulfide is subsequently removed in an absorber and hydrogen is compressed and recirculated to be used as interbed quench, as well as mixed with vacuum gas oil feed.
The liquid effluent of the hot high pressure separator, which may contain materials boiling in the diesel range, is also passed to the fractionator. The fractionator bottoms may be subsequently hydrocracked and products may be subsequently hydrotreated in units not depicted.
This invention offers several notable benefits. The invention provides a method for hydroprocessing two refinery streams using a single hydrogen supply and a single hydrogen recovery system. Furthermore, the instant invention provides a method for hydrocracking a refinery stream and hydrotreating a second refinery stream with a common hydrogen feed supply. The feed to the hydrocracking reaction zone is not poisoned with contaminants present in the feed to the hydrotreating reaction zone. The present invention is further directed to hydroprocessing two or more dissimilar refinery streams in an integrated hydroconversion process while maintaining good catalyst life and high yields of the desired products, particularly distillate range refinery products. Such dissimilar refinery streams may originate from different refinery processes, such as a VGO, derived from the effluent of a VGO hydrotreater, which contains relatively few catalyst contaminants and/or aromatics, and an FCC cycle oil or straight run diesel, which contains substantial amounts of aromatic compounds.